Motor vehicles employ heat exchangers to heat or cool various elements of an automotive engine and its component parts. UK Patent application GB 2166862 A, published May 14, 1986, Gebhard Schwarz, ‘Vehicle radiator’ discloses a radiator constituted by flat tubes and a single water containing header with separating webs in the flat tubes which extend in prolongation of the separating wall in the water container. U.S. Pat. No. 4,023,618 issued on May 17, 1977, Kun et al, ‘Heat exchanger headering arrangement,’ discloses a heat exchanger assembly comprising a stacked array of thin-walled heat exchange channel elements. The headering arrangement includes a resilient gasket disposed around the perimeter of each face against the wall portion ends thereof and header tank means enclosing each face of the array and forms a fluid tight seal between the header tank and the stacked array. U.S. Pat. No. 6,179,049 issued Jan. 30, 2001, Higgins, ‘Head exchanger with an integrated tank and head sheet,’ discloses a heat exchanger having a core of a plurality of cooling tubes with a tank at each end of the core tubes. The tanks are formed with a plurality of cooling tube receiving apertures along a side portion of the tanks which receive the ends of the cooling tubes directly into the tanks and are attached to the tubes by brazing. U.S. Pat. No. 4,183,402 issued Jan. 15, 1980, Cotter, ‘Heat exchanger heardering arrangement,’ discloses a heat assembly comprising a stacked array of heat exchange channel elements. The improved headering arrangement includes sealing members each having a bearing surface with a generally corrugated contour and header tank means joined to the sealing members so as to leak-tightly enclose the associated face of the stacked array of heat exchange channel elements. Heat exchangers employ heat exchanger tanks which typically include a coolant and require a fluid tight seal. Heat exchanger tanks may be made of a variety of materials, depending on the strength and/or temperature requirements imposed upon them in automotive applications. Plastic tanks have been utilized in heat exchangers and have proven to reduce weight while providing good thermal and strength characteristics in a number of applications. In certain commercial heat exchangers and automotive radiators, it has been common practice to employ a tube sheet headering arrangement.
In such systems, the tubes in the heater core assembly are characteristically forced through corresponding size openings in a sheet member and the latter is then joined to suitable tank or shell means to form a ‘header’ or header chamber communication with the tubes of the core assembly for introduction or withdrawal of fluid being passed through the tube members.
In certain state of the art designs for automotive heat exchangers with plastic tanks, headers that are stamped from an aluminum sheet are used. In such designs, tube slots are formed with ‘ferrules’ or ‘collars’ in the header to accept tubes and to provide a mating surface for brazing the tubes to the header.
As described above, such tank-header arrangements require a fluid tight seal. In order to create such a seal, a depression or trough is formed around the periphery of the header to accommodate the ‘edge flange’ or ‘foot’ of the plastic tank; which also serves to retain a header gasket that provides a seal between the tank and header. Correspondingly, the header further includes an oppositely directed ‘depression’ or ‘pan’ within the periphery of the outer trough. In certain prior art heat exchangers, the edges of the plastic tank are molded to the turned flange or foot. During construction of the heat exchanger, the tank is installed in the trough, with the tank foot compressing the gasket. The outer edges of the aluminum header are then bent or ‘crimped’ to capture the edge of the tank foot, thereby joining the tank to the header (See prior art FIG. 1). However, due to the strict requirements imposed upon use of such plastic tanks in automotive applications, and the need to provide fluid tight seals, designs for plastic heat exchanger tanks also use ‘flanges’ or ‘feet’ that fit inside the trough formed around the periphery of the header.
In addition, different heat exchanger applications are subjected to different internal pressure and related conditions. Radiators typically have lower operating pressures and temperatures than charge-air-coolers. Radiator tanks can generally be more compact, since the internal fluid is a higher density liquid. Charge air coolers, inter coolers and after coolers typically operate at higher temperatures and pressures, and with more rapid transients than radiators in the same vehicle application. Higher pressures and larger wall surface areas result in greater wall deflection in such applications. Higher temperatures reduce the stiffness and fatigue resistance of the materials. These factors contribute to greater structural integrity and durability problems with more extreme temperatures and pressure conditions.
Reinforcing ribs are also been used on the header of heat exchanger between tube slots (See FIG. 2). Recently a so-called all-aluminum heat exchanger has been invented that provides for brazing of the inner flange of the header to the ends of the tube as an option when utilizing plastic tanks. See US Patent application 2003/0217838A1 published Nov. 27, 2003, Dey et al.
Problems identified in the prior art, therefore, include that of a trough (or well) formed in the periphery of the header tends to increase the overall thickness of the heat exchanger, which can result in packaging problems in the vehicle; and, that of a header width also creates a bending moment, as the offset of the gasket (lower) flange from the header plane generates a second bending moment. These bending moments contribute to stress concentrations in the header when internal pressure is applied. Moving the inner flange inward such that it contacts and is brazed to the tube improve packaging. However, the solution of connecting the inner flange to the thin-walled tube can create stress concentrations in the tube under internal pressure which may exceed acceptable limits in some applications. This, in addition to the problem of internal temperature and pressure conditions in heat exchanger applications, require further solutions not yet found in the prior art.
One response to these conditions has been to provide more rigid tanks and headers for extreme temperature and/or pressure heat exchanger applications. Tank and header deflection and corresponding stresses can lead to failure in the tank wall, in the header, or in the tube-to-header joint area.
Even in a case of radiators, in the initial vacuum coolant filling of radiators in the factory, extreme internal environmental conditions, such a low internal pressure is required that may pull the radiator tank walls and gasket inward, must be resisted by a reinforced feature such as a header inner flange, or the like.
Solutions such as a brazed flange design would achieve similar compactness, but brazing the inner flange to the tube can create stress concentrations in the tube under pressure loading.
Headering means employing mechanical attachment and sealing methods have been developed, due to the difficulty of effectively welding, brazing or soldering of unlike materials (such as alloy headers with plastics such as those found on radiator header tanks). One solution is to provide for an inner flange that encloses a gasket and tank foot, reducing the tendency of the latter to rotate under internal pressure. While this design has been found to be adequate for many radiator applications, it has many disadvantages which are accentuated, as described above, when used in more extreme, and, particularly, internal high temperature and pressure conditions, such as those found in charge air coolers and the like. The present invention has even further advantages as it relates to heat exchangers when fluid flow involves lower density liquids or where operating pressures are greater than moderate or even high to very high.